The present invention relates to methods and apparatuses for planarizing microelectronic substrate assemblies and, more particularly, to apparatuses and methods for endpointing mechanical and/or chemical-mechanical planarization of semiconductor wafers, field emission displays and other microelectronic substrate assemblies.
Mechanical and chemical-mechanical planarizing processes (collectively xe2x80x9cCMPxe2x80x9d) are used in the manufacturing of electronic devices for forming a flat surface on semiconductor wafers, field emission displays and many other microelectronic substrate assemblies. CMP processes generally remove material from a substrate assembly to create a highly planar surface at a precise elevation in the layers of material on the substrate assembly.
FIG. 1 is a schematic isometric view of a web-format planarizing machine 10 for planarizing a microelectronic substrate assembly 12. The planarizing machine 10 has a table 11 with a rigid panel or plate to provide a flat, solid support surface 13 for supporting a portion of a web-format planarizing pad 40 in a planarizing zone xe2x80x9cA.xe2x80x9d The planarizing machine 10 also has a pad advancing mechanism including a plurality of rollers to guide, position, and hold the web-format pad 40 over the support surface 13. The pad advancing mechanism generally includes a supply roller 20, first and second idler rollers 21a and 21b, first and second guide rollers 22a and 22b, and a take-up roller 23. As explained below, a motor (not shown) drives the take-up roller 23 to advance the pad 40 across the support surface 13 along a travel axis Txe2x80x94T. The motor can also drive the supply roller 20. The first idler roller 21a and the first guide roller 22a press an operative portion of the pad against the support surface 13 to hold the pad 40 stationary during operation.
The planarizing machine 10 also has a carrier assembly 30 to translate the substrate assembly 12 across the pad 40. In one embodiment, the carrier assembly 30 has a head 32 to pick up, hold and release the substrate assembly 12 at appropriate stages of the planarizing process. The carrier assembly 30 also has a support gantry 34 and a drive assembly 35 that can move along the gantry 34. The drive assembly 35 has an actuator 36, a drive shaft 37 coupled to the actuator 36, and an arm 38 projecting from the drive shaft 37. The arm 38 carries the head 32 via another shaft 39. The actuator 36 orbits the head 32 about an axis Bxe2x80x94B to move the substrate assembly 12 across the pad 40.
The polishing pad 40 may be a non-abrasive polymeric pad (e.g., polyurethane), or it may be a fixed-abrasive polishing pad in which abrasive particles are fixedly dispersed in a resin or another type of suspension medium. A planarizing fluid 50 flows from a plurality of nozzles 49 during planarization of the substrate assembly 12. The planarizing fluid 50 may be a conventional CMP slurry with abrasive particles and chemicals that etch and/or oxidize the surface of the substrate assembly 12, or the planarizing fluid 50 may be a xe2x80x9ccleanxe2x80x9d non-abrasive planarizing solution without abrasive particles. In most CMP applications, abrasive slurries with abrasive particles are used on non-abrasive polishing pads, and non-abrasive clean solutions without abrasive particles are used on fixed-abrasive polishing pads.
In the operation of the planarizing machine 10, the pad 40 moves across the support surface 13 along the pad travel path Txe2x80x94T either during or between planarizing cycles to change the particular portion of the polishing pad 40 in the planarizing zone A. For example, the supply and take-up rollers 20 and 23 can drive the polishing pad 40 between planarizing cycles such that a point P moves incrementally across the support surface 13 to a number of intermediate locations I1, I2, etc. Alternatively, the rollers 20 and 23 may drive the polishing pad 40 between planarizing cycles such that the point P moves all the way across the support surface 13 to completely remove a used portion of the pad 40 from the planarizing zone A. The rollers may also continuously drive the polishing pad 40 at a slow rate during a planarizing cycle such that the point P moves continuously across the support surface 13. Thus, the polishing pad 40 should be free to move axially over the length of the support surface 13 along the pad travel path Txe2x80x94T.
CMP processes should consistently and accurately produce a uniform, planar surface on substrate assemblies to enable circuit and device patterns to be formed with photolithography techniques. As the density of integrated circuits increases, it is often necessary to accurately focus the critical dimensions of the photo-patterns to within a tolerance of approximately 0.1 xcexcm. Focusing photo-patterns to such small tolerances, however, is difficult when the planarized surfaces of substrate assemblies are not uniformly planar. Thus, to be effective, CMP processes should create highly uniform, planar surfaces on substrate assemblies.
In the highly competitive semiconductor industry, it is also desirable to maximize the throughput of CMP processing by producing a planar surface on a substrate assembly as quickly as possible. The throughput of CMP processing is a function of several factors, one of which is the ability to accurately stop CMP processing at a desired endpoint. In a typical CMP process, the desired endpoint is reached when the surface of the substrate assembly is planar and/or when enough material has been removed from the substrate assembly to form discrete components on the substrate assembly (e.g., shallow trench isolation areas, contacts, damascene lines, etc.). Accurately stopping CMP processing at a desired endpoint is important for maintaining a high throughput because the substrate assembly may need to be re-polished if it is xe2x80x9cunder-planarized,xe2x80x9d or too much material can be removed from the substrate assembly if it is xe2x80x9cover-polished.xe2x80x9d For example, over-polishing can cause xe2x80x9cdishingxe2x80x9d in shallow-trench isolation structures or completely destroy a section of the substrate assembly. Thus, it is highly desirable to stop CMP processing at the desired endpoint.
One method for determining the endpoint of CMP processing is described in U.S. Pat. No. 5,036,015 issued to Sandhu (xe2x80x9cSandhuxe2x80x9d), which is herein incorporated by reference. Sandhu discloses detecting the planar endpoint by sensing a change in friction between a wafer and the polishing medium. Such a change of friction may be produced by a different coefficient of friction at the wafer surface as one material (e.g., an oxide) is removed from the wafer to expose another material (e.g., a nitride). In addition to the different coefficients of friction caused by a change of material at the substrate surface, the friction between the wafer and the planarizing medium generally increases during CMP processing because more surface area of the substrate contacts the polishing pad as the substrate becomes more planar. Sandhu discloses detecting the change in friction by measuring the change in electrical current through the platen drive motor and/or the drive motor for the substrate holder.
Although Sandhu discloses a viable process for endpointing CMP processing, the change in electrical current through the platen and/or drive motor may not accurately indicate the endpoint of a substrate assembly. For example, the friction between the substrate assembly and the planarizing medium generally increases substantially linearly, and thus the change in the motor current at the endpoint may not be sufficient to provide a definite signal identifying that the endpoint has been reached. Moreover, friction losses and other power losses in the motors, gearboxes or other components may also change the current draw through the motors. The change in current through the drive motors, therefore, may not accurately reflect the drag force between the wafer and the polishing pad because the drag force is not the only factor that influences the current draw. Thus, it would be desirable to develop an apparatus and method for more accurately endpointing planarization of microelectronic substrate assemblies.
The present invention is directed toward endpointing apparatuses, planarizing machines with endpointing apparatuses, and methods for endpointing mechanical and/or chemical-mechanical planarization of microelectronic substrate assemblies. One endpointing apparatus in accordance with the invention includes a primary support member for supporting either a polishing pad or a substrate assembly, and a secondary support member coupled to the primary support member. The primary support member is movable with respect to the secondary support member in a lateral motion at least generally parallel to a planarizing plane in correspondence to drag forces between the substrate assembly and the polishing pad. The primary support member, for example, can rest on a bearing assembly that provides for relatively frictionless lateral displacement between the primary and secondary support members. The endpointing apparatus also includes a force detector attached to the primary support member and/or the secondary support member at a force detector site having a contact surface transverse to the planarizing plane. The force detector measures lateral forces between the primary support member and the secondary support member in response to drag forces between the substrate assembly and the polishing pad. The primary support member can be held with respect to the secondary support member by dead stops and force detectors, or by posts attached to both the primary and secondary support members. In either case, the force detector senses lateral forces imparted to the primary support member by the substrate assembly during planarization. In operation, the endpoint of CMP processing is detected when the measured lateral force is equal to a predetermined endpoint force for a particular CMP application.
In one planarizing machine in accordance with the invention, the primary support member is a moveable primary plate or platen under the polishing pad, and the secondary support member is a base or sub-platen under the primary plate. The planarizing machine can also include a carrier assembly having a head configured to hold a substrate assembly against the planarizing surface and a drive system to move the head. At least one of the polishing pad or the head moves in a lateral motion at least generally parallel to the planarizing plane. The base can have a base surface facing toward the polishing pad and a first stop surface projecting from the base surface transverse to the planarizing plane. The primary plate can have a bearing surface facing the backside of the polishing pad to support at least a portion of the polishing pad in a planarizing zone, and the primary plate can also have a first contact surface adjacent to the first stop surface on the base. The primary plate is moveable with respect to the base in a lateral motion corresponding to the drag forces between the substrate assembly and the polishing pad. The planarizing machine can further include at least a first force detector contacting the first stop surface and the first contact surface at a load site. The force detector is configured to sense lateral forces between the base and the primary plate corresponding to the lateral drag forces between the substrate assembly and the polishing pad.
The present invention also includes several additional embodiments in which the force detector is attached at a load site to at least one of the carrier head or the table. Several of these embodiments accordingly do not use a table with primary and secondary support members. The force detector provides a signal indicative of the lateral drag forces between the substrate assembly and the polishing pad.